This invention relates generally to microwave hyperthermia treatment systems and, more particularly, to a microwave phase shifter suitable for use in such systems.
Continuous microwave phase shifters utilizing variable reactive loads on the reflection ports of 3 decibel (dB) quadrature hybrid couplers are known in the art and have been utilized primarily as phase modulators. This application requires that the phase shifters provide a linear phase versus control voltage relationship, as well as broadband frequency response characteristics. The maintenance of a substantially uniform insertion or transmission loss over the range of available phase shift is, however, only of secondary concern.
In microwave hyperthermia treatment systems, which typically operate at a single fixed frequency, broadband frequency response characteristics are not required, nor is it required that a phase shifter used in such a system exhibit a linear phase versus control voltage response. Rather, a substantially uniform transmission loss over the range of available phase shift is the Primary design goal. Accordingly, phase shifters which are well suited for use as phase modulators are generally not as well suited for use in microwave hyperthermia treatment systems. Furthermore, such phase shifters are generally of greater complexity than is necessary for use in a microwave hyperthermia treatment system and can needlessly raise the cost of such a system.
In view of the foregoing, it is a general object of the present invention to provide a new and improved continuous microwave phase shifter.
It is a further object of the present invention to Provide a new and improved phase shifter which provides a substantially uniform transmission loss over the range of available phase shift and is thus well suited for use in a hyperthermia treatment system.
It is a still further object of the present invention to provide a continuous microwave phase shifter which can be manufactured with economy and ease.